System and method for beamforming wth automatic amplitude and phase error calibration

ABSTRACT

The present disclosure provides a method for performing beamforming. The method includes initiating a first signal transmitted from a target second device to be received by a first device having an antenna array. A first beamforming weight matrix is generated by the first device that automatically corrects amplitude and phase errors of the antenna array and maximizes antenna gain toward the target second device using a covariance matrix derived from the received first signal. An enhanced second beamforming weight matrix is then generated by the first device using a mask window or a jointly optimized algorithm to further suppress interference to and from other active second devices. The enhancement is computed and applied based on the distribution of multiple active second devices. The antenna array is steered using the second beamforming weight matrix to transmit to and receive from the target second device with an optimized antenna beam pattern.

CROSS REFERENCE

This application claims the benefit of U.S. Provisional Application Ser.No. 62/262,930, filed on Dec. 4, 2015, and entitled “SYSTEM AND METHODFOR BEAMFORMING WITH AUTOMATIC AMPLITUDE AND PHASE ERROR CALIBRATION”,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject matter herein generally relates to multiple-inputmultiple-output (MIMO) communication, in particular, to a system and amethod for improving the beamforming performance using an antenna array.

BACKGROUND

Beamforming is a common communication technique used in wirelesscommunication systems, in which an array of antennas is used to formrespective beams to transmit or receive signals in such a manner that indirections of target devices, the antenna array creates constructivecombining as the array directs towards other devices, and formsdestructive cancellation. The beamforming device, such as a basestation, mobile station, remote radio head (RRH) or any othertransmitting and receiving device, can control the relative phase andamplitude of the signal from each transmitting/receiving antenna elementto create a radiation pattern with the energy focused in a particularbeam at a chosen direction to the targeted receiving device, rather thantransmitting signals in all directions by using beamforming technique.

While a beamforming device using beamforming techniques performs signaltransmission and reception in a multiuser communication system,radiation patterns typically include a mainlobe and one or moresidelobes. While the mainlobe is pointing toward the target device, thesidelobes are in general transmitted in all directions, causinginterference with other active devices and lowering the overallefficiency in the communication system.

SUMMARY

Accordingly, the present disclosure provides a beamforming technique forefficiently and accurately determining beamforming weight for an antennaarray (e.g. a digital antenna array) to improve the efficiency of thecommunication system and to increase the ability to service more userdevices (e.g., mobile stations).

Disclosed are systems, methods and computer-readable media for providinga beamforming technique that enables accurate beamforming weightdetermination for an antenna array, and at the same time automaticallycalibrates amplitude and phase errors across antenna elements of theantenna array.

An exemplary embodiment of the present disclosure provides a method forperforming communication between a first device and a plurality ofsecond devices. The first device is generally considered stationary(e.g., a base station or a remote radio head) and communicates with anumber of different second devices, which can be mobile user equipment,mobile stations, or the equivalent. The first device is equipped with anantenna array. Each of the second devices is equipped with at least oneantenna. The first device and the second device are communicating in aTime Division Duplex (TDD) communication system, where an uplink and adownlink transmission are performed on the same frequency channel.

The method is illustrated as follows. The first device receives a signaltransmitted from one of the second devices. Next, the first devicecomputes a covariance matrix based on the received signal. The firstdevice subsequently generates a first beamforming weight matrixassociated with the antenna array using the covariance matrix computed.The first device further adjusts the first beamforming weight matrix togenerate a second beamforming weight matrix corresponding to the seconddevice using a mask window. The mask window can be configured based onthe distance separation between the targeted second device and theadjacent second devices. Thereafter, the first device operatively steersthe antenna array based on the second beamforming weight matrix tocommunicate with the targeted second device.

Another exemplary embodiment provides a beamforming control system fordriving an array of antennas of a first device to generate a beamformingradiation pattern with respect to a second device in communication basedon a signal received from the second device using the array of antennas.In the present embodiment, the second device can be a mobile device,which is operable to select an application at startup. The first devicecan be, for example, a base station, or a remote radio head (RRH).

The system at least includes a processor and a memory. The memory hasstored instructions, which when executed by the processor, causes theprocessor to perform steps of, generating a first beamforming weightmatrix based on a signal transmitted to the first device from one of thesecond devices communicating with the first device; applying a maskwindow adjusting the first beamforming weight matrix to generate asecond beamforming matrix, wherein the mask window is configured basedon the tradeoff between the beam-width of main lobe and the sideloberejection level; steering the antenna array using the second beamformingweight matrix to form a beam toward a direction of the second device.

In one embodiment, the first device generates the first beamformingweight matrix using a sub-space Singular Value Decomposition (SVD)algorithm from the covariance matrix computed.

In one embodiment, the first device generates the first beamformingweight matrix using a noise corrected cross correlation vector from thecovariance matrix computed.

In at least one embodiment, the first device computes the secondbeamforming weight matrix corresponding to the targeted second devicesby applying a Chebyshev window to uniformly suppress the sidelobeemissions to a desired level.

In another aspect, the present disclosure provides a beamforming device,and the beamforming device includes an antenna module, and a beamformingcontroller. The beamforming device is operated under a massivemultiple-input and multiple-output (MIMO) system, particularly operatedunder a TDD MIMO data communication system.

The antenna module is configured to connect to the beamformingcontroller. The antenna array is configured to operatively form aradiation beam pattern to transmit and receive signal in a specificdirection. The antenna module comprises an M by N antenna array. In oneembodiment, the antenna module is an M by 1 antenna array, where M is aninteger lying between 2 to 256.

The beamforming controller includes a phase and amplitude errorcalibration module, a mask window generator, and a beamforming controlmodule. The mask window generator is coupled to the phase and amplitudeerror calibration module. The beamforming control module is coupled tothe mask window generator.

The phase and amplitude error calibration module is configured tocompute the covariance matrix based on a signal received from a mobileuser equipment by each element of the antenna array, so as to generatethe first beamforming weight matrix. The mask window generator isconfigured to generate a mask window based on the separation between theuser equipment and adjacent user equipment, and apply the mask window tothe first beamforming matrix to generate a second beamforming weightmatrix. The beamforming control module is configured to control theradiation pattern generated by the antenna array for performingtransmission and reception operation with the respective user equipmentaccording to the second beamforming weight matrix.

In at least one embodiment, the beamforming device is configured tocompute the second beamforming weight matrices after all the firstbeamforming weight matrices associated with all the second devicescommunicating with the beamforming device have been determined. Thebeamforming device operatively computes the second beamforming weightmatrices for all the second devices based on all the first beamformingweight matrices in such a manner that the sidelobe emissions can bejointly and accurately suppressed in undesired directions toward othersecond devices while the main beam toward the targeted second device ismaximized. As more second devices are able to share the same frequencyband, the overall network efficiency is further optimized. In at leastone embodiment, the beamforming device computes the second beamformingweight matrix using a zero-forcing (ZF) algorithm. In anotherembodiment, the beamforming device computes the second beamformingweight matrix using a maximum ratio combining (MRC) algorithm. In stillanother embodiment, the beamforming device computes the secondbeamforming weight matrix using a combination of the ZF algorithm andthe MRC algorithm.

The following descriptions and appended drawings are referred to suchthat, all the purposes, features, and aspects of the present disclosurecan be understood. However, the appended drawings are merely providedfor reference and illustration, with no intention of limiting the scopeof the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the present disclosure and, together with thedescription, serve to explain the principles of the present disclosure.

FIG. 1 is a diagram illustrating a communication system in accordance toan exemplary embodiment of the present disclosure.

FIG. 2 is a diagram illustrating an arrangement for an antenna arrayused for a communication system in accordance to an exemplary embodimentof the present disclosure.

FIG. 3 is a flowchart diagram illustrating a beamforming method inaccordance to an exemplary embodiment of the present disclosure.

FIG. 4 is a diagram illustrating a communication system in accordance toanother exemplary embodiment of the present disclosure.

FIG. 5A and FIG. 5B are diagrams each illustrating a beamformingradiation pattern for one mobile user equipment in accordance to anexemplary embodiment of the present disclosure.

FIG. 6 is a block diagram illustrating a base station architecture inaccordance to an exemplary embodiment of the present disclosure.

FIG. 7 is a diagram illustrating a communication system in accordance toanother exemplary embodiment of the present disclosure.

FIG. 8 is a flowchart diagram illustrating a beamforming method inaccordance to another exemplary embodiment of the present disclosure.

FIG. 9A and FIG. 9B are diagrams each illustrating beamforming radiationpatterns for two mobile user equipment in accordance to anotherexemplary embodiment of the present disclosure.

FIG. 10A and FIG. 10B are diagrams each illustrating beamformingpatterns for four mobile user equipment in accordance to anotherexemplary embodiment of the present disclosure.

FIG. 11 is a flowchart diagram illustrating a beamforming method inaccordance to another exemplary embodiment of the present disclosure.

FIG. 12A and FIG. 12B are diagrams each illustrating beamformingpatterns for two mobile user equipment using zero-forcing algorithm inaccordance to another exemplary embodiment of the present disclosure.

FIG. 13A and FIG. 13B are diagrams each illustrating beamformingpatterns for four mobile user equipment using zero-forcing algorithm inaccordance to another exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described.

The drawings are not necessarily to scale and the proportions of certainparts may be exaggerated to better illustrate details and features. Thedescription is not to be considered as limiting the scope of theembodiments described herein.

The term “comprising” means “including, but not necessarily limited to”;it specifically indicates open-ended inclusion or membership in aso-described combination, group, series, and the equivalents. The term“coupled” is defined as connected, whether directly or indirectlythrough intervening components, and is not necessarily limited tophysical connections.

Beamforming has been applied in various forms in standards such as 2G,3G, Long Term Evolution (LTE) or 4G technologies. It is expected thatbeamforming will be part of more advanced standards such as the 5Gstandards.

In order to accurately compute beamforming weights to optimize theperformance of an antenna array, it is required that the undesiredamplitude and phase variations across each antenna array element bemeasured, tabulated, updated periodically while corrections are appliedto compensate the undesired amplitude and phase variation in eachbeamforming weight computation. The present disclosure describes amethodology that can accurately compute beamforming weights fromsub-space decomposition with amplitude and phase error correctionsautomatically included, thereby improving the efficiency of thecommunication system and increasing the ability to service more userdevices (e.g., user equipment, mobile stations).

A system, method and computer-readable storage devices are disclosed forproviding an improved beamforming approach applicable to the evolving 5Gindustry standard. Beamforming is anticipated to be used widely in 3rdGeneration Partnership Project (3GPP) applications to enhance thenetwork throughput performance, so as to increase the overall userexperience.

A plurality of antennas will be needed to perform beamforming. As powerand processing capability become available, sufficient number ofantennas (e.g., 2-256 or more antennas) may deploy, to enable thecreation of more focused beams with lower sidelobe level.

Embodiments disclosed herein include devices such as RRHs or basestations that include an array of antennas and communicate with a numberof mobile devices. Other embodiments can include a mobile device or anequivalent device that is capable of communicating with another mobiledevice. Examples of mobile devices can be a smartphone, a laptop or atablet. Yet other embodiments disclosed herein include methods practicedon a beamforming device (whether a device is stationary, such as a basestation, or a mobile device, such as a smart phone) related to theimplementation of beamforming operations.

FIG. 1 shows a diagram illustrating a massive multiple-inputmultiple-output (MIMO) communication system provided in accordance to anexemplary embodiment of the present disclosure. A massive MIMOcommunication system 1 includes a stationary station 10 (e.g., a basestation, or a RRH) and mobile devices 22, 24, 26. The stationary station10 is equipped with a plurality of antennas 101 arranged in an arrayform (e.g., M by N antenna array).

In the instant embodiment, the number of antennas associated with thestationary station 10 may be ranging from 2 to 256 antennas dependingupon the application requirement. For example, a repeater, a basestation, or a RRH may use 32-256 antennas. As the number of antennasincreases, the ability of the system to transmit a focused beam ofenergy in a particular direction increases. Each of the mobile devices22, 24, and 26 is equipped with at least one antenna. Similarly,depending on the application of the mobile device, the mobile devices22, 24, and 26 may be equipped with one or more antennas. For instance,a handheld device, such as a smartphone, may have 1-8 antennas, while avehicle may have 1-32 antennas. In the instant embodiment, the massiveMIMO communication system 1 is a Time Division Duplex (TDD) datatransmission system, i.e., the communications between the stationarydevice 10 and each of the mobile devices 22, 24, 26 are performed in thesame frequency band.

Beams 221, 241, and 261 illustrate three beams of electromagneticenergy, in the same or different frequencies, formed by an antennamodule of the stationary station 10 in a beamforming operation. Beams221, 241, and 261 are focused in the respective directions of the mobiledevices 22, 24, and 26. Data communication between each of the mobiledevices 22, 24, 26 and the stationary station 10 may interfere with oneanother mobile devices depending upon the separation angle (e.g., theazimuth angle) between adjacent mobile devices if the same frequency isused for all mobile devices 22, 24, 26. For instance, the beam 241formed to establish a data communication channel between the stationarystation 10 and the mobile device 24 may be interfered by sidelobesassociated with beams 221 and 261. The stationary station 10 is operableto accurately determine beamforming weights to form beams 221, 241, and261 in respective directions while being able to suppress or mitigatethe sidelobe emission effect to neighboring mobile devices, therebyimproving the bandwidth efficiency and optimizing the network efficiencyof the massive MIMO communication system 1, and more user devices canthus share the same frequency band.

The existence of sidelobes of energy is omitted from FIG. 1 forsimplicity, which will typically have much lower power levels than themain beams and are to the left and/or right of any particular beam. Itshould be noted that sidelobes associated with each of the main beamsare omitted from FIG. 1 for simplicity, where the sidelobes typicallyhave much lower power levels than the main beams.

FIG. 2 is a perspective view illustrating an exemplary embodiment of anantenna array arrangement to be used by the stationary station 10 forperforming beamforming operations. In the instant embodiment, an antennaarray 200 for the antenna module is a 16 by 4 antenna array and includes64 antenna elements A1 through A64. The bore-sight axis (i.e., the axisof maximum gain of the antenna array 200) is facing toward the positiveY-direction. The space between any two adjacent antenna elements alongthe X-direction is represented by d_(x), and the space between any twoadjacent antenna elements along the Z-direction is represented by d_(z).An incident angle φ associated with an incident signal is measured inthe azimuth direction and represents the steering angle of the antennaarray from the positive X-direction in the X-Y plane. An elevation angleθ is a tilt down angle between the incident signal and the positiveZ-axis.

In practice, the antenna array for the stationary station 10 may be anyM by N antenna array, such as a 64 by 1 antenna array, an 8 by 8 antennaarray, or the like, depending on the operation requirements of thestationary station 10, and the present disclosure is not limitedthereto.

Referring to FIG. 3 in conjunction to FIG. 4. FIG. 3 illustrates abeamforming method applicable to the massive MIMO communication system 1of FIG. 1, which is a TDD-based communication system, provided inaccordance to an exemplary embodiment of the present disclosure. FIG. 4illustrates a beamforming operation. In the instant embodiment, thebeamforming method illustrated is an application to the massive MIMOcommunication system, in which a first device communicates with onemobile station at a time.

One embodiment relating to the method depicted in FIG. 3 can beimplemented by the first device such as a base station or a RRH, or anystationary station. The first device is generally considered the devicethat is stationary and communicates with a number of different seconddevices, which can be mobile stations or mobile user equipment or thelike. The first device is equipped with an antenna array comprising aplurality of antenna elements, and the number of antenna elements canrange between 2 and 256 antenna elements. In the instant embodiment, theantenna array is an M by 1 antenna array, for instance, a 64 by 1antenna array. M herein is an integer and in the instant embodimentrepresents the total number of antenna elements (e.g., 64) in the M by 1antenna array.

At block 301, a first device (e.g., a base station 40) receives a firstsignal r(t) transmitted by a second device (e.g., a mobile station 44).The amplitude and phase errors associated with the antenna elements ofthe antenna array in response to the signal are unknown and these errorsare shown with the received signal. The signal r(t) with unknownamplitude and phase errors may be represented by Eq. (1)

$\begin{matrix}{{{r(t)} = {\begin{bmatrix}{r_{0}(t)} \\\vdots \\{r_{k}(t)} \\\vdots \\{r_{({M - 1})}(t)}\end{bmatrix} = {{\begin{bmatrix}{A_{0}e^{j\;\theta_{0}}s_{0}} \\\vdots \\{A_{k}e^{j\;\theta_{k}}s_{k}} \\\vdots \\{A_{({M - 1})}e^{j\;\theta_{({M - 1})}}s_{M - 1}}\end{bmatrix}*{x(t)}} + \begin{bmatrix}{n_{0}(t)} \\\vdots \\{n_{k}(t)} \\\vdots \\{n_{({M - 1})}(t)}\end{bmatrix}}}}{where}{{s_{k} = e^{\frac{j\; 2\pi\;{kd}\;\sin\;\phi}{\lambda}}},}} & (1)\end{matrix}$wherein r(t) represents the signal received by the first device;n_(k)(t) represents the noise received by the kth antenna element; A₀through A_((M-1)) represent the amplitude errors of the signal receivedby the antenna elements 0 to (M−1); θ₀ through θ_((M-1)) represent thephase errors the antenna elements 0 to (M−1); x(t) represents the signalactually transmitted by the second device (e.g., the mobile station 44);s_(k) is the array steering vector toward the transmitting device,wherein k is an integer ranging between 0 to M−1; d is the separationdistance between antenna elements, λ is a wavelength and □ is incidentangle.

At block 303, the first device generates a covariance matrix Rreflecting the channel characteristic between the first device (e.g.,the base station 40) and the second device (e.g., the mobile station 44)based on the received signal r(t). In at least one embodiment, thesignal r(t) may be an uplink signal from the second device (e.g., themobile station 44) such as a reference signal, a pilot signal, or anactual data signal.

The first column (or a cross correlating vector R₀) of covariance matrixR, corresponds to the channel between the first device and the targetedsecond device (e.g., the mobile station 44), is computed by crosscorrelating the received signal r_(k) at each of the M antennas with thesignal r₀ received at the first antenna. The amplitude error A_(k), thephase error θ_(k) and the steering vector s_(k) can be jointly estimatedfrom Eq. (1.1), using the cross correlations of signals received atdifferent antenna elements.

$\begin{matrix}{{R = \begin{bmatrix}R_{0} & R_{1} & R_{2} & \ldots & R_{({M - 1})}\end{bmatrix}}{R_{0} = {\begin{bmatrix}{E\lbrack {r_{0}r_{0}^{\prime}} \rbrack} \\\vdots \\{E\lbrack {r_{k}r_{0}^{\prime}} \rbrack} \\\vdots \\{E\lbrack {r_{({M - 1})}r_{0}^{\prime}} \rbrack}\end{bmatrix} = {{A_{0}{{E\lbrack {xx}^{\prime} \rbrack} \cdot \begin{bmatrix}{{A_{0}e^{j(\;{\theta_{0} - \theta_{0}})}s_{0}s_{0}^{\prime}} + {E\lbrack {nn}^{\prime} \rbrack}} \\\vdots \\{A_{k}e^{j\;{({\theta_{k} - \theta_{0}})}}s_{k}s_{0}^{\prime}} \\\vdots \\{A_{({M - 1})}e^{j\;{({\theta_{({M - 1})} - \theta_{0}})}}s_{M - 1}s_{0}^{\prime}}\end{bmatrix}}} = {Z \cdot \begin{bmatrix}{{A_{0}e^{j\;\theta_{0}}s_{0}} + \sigma_{n}^{2}} \\\vdots \\{A_{k}e^{j\;\theta_{k}}s_{k}} \\\vdots \\{A_{({M - 1})}e^{j\;\theta_{({M - 1})}}s_{M - 1}}\end{bmatrix}}}}}{where}{{Z = {A_{0}e^{{- j}\;\theta_{0}}s_{0}^{\prime}{E\lbrack {xx}^{\prime} \rbrack}}};}{{\sigma_{n}^{2} = {E\lbrack {nn}^{\prime} \rbrack}},}} & (1.1)\end{matrix}$wherein R represents the covariance matrix computed; R₀ represents thecross correlating vector associated with the first antenna element;r₀(t) signal received by the first antenna element; n_(k)(t) representsthe noise received by the kth antenna element; A₀ through A_((M-1))represent the amplitude errors of the signal received by the antennaelements 0 to (M−1); θ₀ through θ_((M-1)) represent the phase errors ofthe antenna element 0 to (M−1); s_(k) is the array steering vectortoward the transmitting device; σ_(n) ² represents the noise covariance;k is an integer ranging between 0 to M−1; d is the separation distancebetween antenna elements.

At block 305, the first device (e.g., the base station 40) generates afirst beamforming weight matrix w₁ associated with each of the antennaelements of the antenna array based on the covariance matrix R. Thefirst beamforming weight matrix w₁ comprises of M by 1 beamformingweight coefficients, and each of the beamforming weight coefficients isassociated with a corresponding one of the antenna elements.

In one embodiment, the first device (e.g., the base station 40) computesthe first beamforming weight matrix w₁, which is generated based on thecovariance matrix R using Singular Value Decomposition (SVD) algorithm.For example, the first beamforming weight matrix w₁ can be computedusing Eq. (2) shown below,

$\begin{matrix}{{w_{1} = {\begin{bmatrix}w_{0} \\\vdots \\w_{k} \\\vdots \\w_{M - 1}\end{bmatrix} = {\begin{bmatrix}\frac{g_{0}^{\prime}}{{g_{0}}^{2}} \\\vdots \\\frac{g_{k}^{\prime}}{{g_{k}}^{2}} \\\vdots \\\frac{g_{M - 1}^{\prime}}{{g_{M - 1}}^{2}}\end{bmatrix} = \begin{bmatrix}{\frac{1}{A_{0}}e^{{- j}\;\theta_{0}}s_{0}^{\prime}} \\\vdots \\{\frac{1}{A_{k}}e^{{- j}\;\theta_{k}}s_{k}^{\prime}} \\\vdots \\{\frac{1}{A_{({M - 1})}}e^{{- j}\;\theta_{({M - 1})}}s_{({M - 1})}^{\prime}}\end{bmatrix}}}},} & (2)\end{matrix}$wherein w₁ represents the first beamforming weight matrix, and w₀ . . .w_(M-1) represent weight coefficient associated with each correspondingantenna element; g=[g₀ g₁ . . . g_(M-1)]^(T) represents the Eigen vectorassociated with the largest Eigen value;

$s_{k} = e^{\frac{j\; 2\pi\;{kd}\;\sin\;\phi}{\lambda}}$represents the steering factor of the array antenna toward the incidentsignal.

Alternatively, the first device can generate the first beamformingweight matrix w₁ associated with each antenna elements of the antennaarray using Eq. (1.1) with the first column (or the cross-correlationvector R₀) of covariance matrix R having noise variance estimationsubtracted from the first entry (e.g., the covariance coefficientE[r₀r₀′]), wherein the noise variance is estimated based on the signalr(t) received from the targeted second device (e.g., mobile station 44).In other words, instead of having performing the computation intensiveSVD algorithm and obtaining the Eigen vector associated with the largestEigen value, the vector g for Eq. (2) can be computed and generated bycorrecting the noise variance in the cross correlation vector R₀, whichis a single column of the covariance matrix, as depicted in Eq. (2.1)

$\begin{matrix}{g = {R_{0} - \begin{bmatrix}{Z\;\sigma_{n}^{2}} \\0 \\\vdots \\\vdots \\0\end{bmatrix}}} & (2.1)\end{matrix}$wherein g represents a cross correlation vector R₀ having noise variancesubstrate; Zσ_(n) ² represents the noise variance estimated for thereceived signal r(t). The first beamforming weight matrix w₁ is thengenerated using Eq. (2) in the similar way as the vector g is generateby the SVD algorithm.

Moreover, at block 305, by computing the first beamforming weight matrixw₁ using either the SVD algorithm or using Eq. (2.1) for beamformingoperation, the unknown amplitude and phase errors associated with theantenna elements in response to the signal received r(t) can becompensated at the same time without calibration. That is, the receivedsignal after beam-forming is a coherent combination of the transmittedsignal x(t) from the second device received at all the antenna elementswith different amplitudes and phases, it can be computed using Eq. (3),wherein M represents the number of antenna elements in the antennaarray.

$\begin{matrix}{{w_{1}^{T}{r(t)}} = {{{\begin{bmatrix}{\frac{1}{A_{0}}e^{{- j}\;\theta_{0}}s_{0}^{\prime}} \\\vdots \\{\frac{1}{A_{k}}e^{{- j}\;\theta_{k}}s_{k}^{\prime}} \\\vdots \\{\frac{1}{A_{({M - 1})}}e^{{- j}\;\theta_{({M - 1})}}s_{({M - 1})}^{\prime}}\end{bmatrix}^{T}\begin{bmatrix}{A_{0}e^{j\;\theta_{0}}s_{0}} \\\vdots \\{A_{k}e^{j\;\theta_{k}}s_{k}} \\\vdots \\{A_{({M - 1})}e^{j\;\theta_{({M - 1})}}s_{M - 1}}\end{bmatrix}}*{x(t)}} = {{Mx}(t)}}} & (3)\end{matrix}$

At block 307, the first device (e.g., the base station 40) adjusts thefirst beamforming weight matrix w₁ by applying an adjustable mask windowbased on the channel condition and the mobile station distribution, soas to generate a second beamforming weight matrix w₂. The secondbeamforming weight matrix can be described using Eq. (4),

$\begin{matrix}{{w_{2} = {\begin{bmatrix}{C_{0}w_{0}} \\\vdots \\{C_{k}w_{k}} \\\vdots \\{C_{M - 1}w_{M - 1}}\end{bmatrix} = \begin{bmatrix}{\frac{C_{0}}{A_{0}}e^{{- j}\;\theta_{0}}s_{0}^{\prime}} \\\vdots \\{\frac{C_{k}}{A_{k}}e^{{- j}\;\theta_{k}}s_{k}^{\prime}} \\\vdots \\{\frac{C_{M - 1}}{A_{({M - 1})}}e^{{- j}\;\theta_{({M - 1})}}s_{({M - 1})}^{\prime}}\end{bmatrix}}},} & (4)\end{matrix}$wherein w₂ represents the second beamforming weight matrix; C=[C₀ C₁ . .. C_(M-1)] represents the mask window with length M.

In the instant embodiment, the mask window is configured according tothe Signal to Interference plus Noise Ratio (SINR) requirement andseparation between adjacent mobile stations to minimize the interferencefrom sidelobe emissions of adjacent mobile stations. For instance, themobile station 44 in FIG. 4 is located along the boresight axisdirection (e.g., at an azimuth angle of 0) with respect to the antennaarray of the base station 40. The mobile station 42 is located anazimuth angle of at ψ1 from the boresight axis. The base station 40 ofFIG. 4 (i.e., the first device) can generate the second beamformingmatrix w₂ corresponding to the position of the mobile station 44 (i.e.,the targeted second device) by applying the mask window based on theseparation (e.g., azimuth angle) between the mobile station 42 and themobile station 44 with respect to the base station 40. The mask windowcan be configured based on the tradeoff between the beam width of themain beam and the sidelobe rejection level.

In one embodiment, the mask window can be implemented by a Chebyshevwindow for minimizing or suppressing the sidelobe interferences, whereinthe Chebyshev window is configured based on the channel condition andthe mobile station distribution.

In one embodiment, the mask window can be implemented by a finiteimpulse response (FIR) filter.

FIG. 5A illustrates a beamforming radiation pattern 501 representing abeam formed by the antenna array of the first device in the direction ofthe targeted mobile station (e.g., the mobile station 44 of FIG. 4),wherein the antenna array is steered using the first beamforming weightmatrix, i.e., without applying the mask window. FIG. 5B illustrates abeamforming radiation pattern 503 representing a beam formed by theantenna array of the first device in the direction of the targetedmobile station (e.g., the mobile station 44 of FIG. 4), wherein theantenna array is steered using the second beamforming weight matrix withsidelobe being suppressed to a desired level (e.g., −35 dB with respectto the main beam). In the meantime, as the result of trade-off, it isobserved that the main beam width is thus widen using the secondbeamforming weight matrix as compared to the width of the main beam inthe radiation pattern 501.

At block 309, the antenna array of the first device is steered accordingto the second beamforming weight matrix to form a specific beamformingpattern toward the specific direction of the targeted second device(e.g., the mobile station 44) for performing data transmission andreception operations.

Under the signal transmission operation, the first device can pre-codethe signal to be transmitted to the targeted second device (e.g., themobile station 44) using the second beamforming weight matrix and steerthe antenna array to transmit the pre-coded signal to the targetedsecond device. Under the signal reception operation, the first devicesteers the antenna array to form a reception beam pattern toward thetargeted second device to receive the signal transmitted by the targetedsecond device.

In the instant embodiment, the first device is a base station and thesecond device is a mobile device. In another example, the first deviceis a mobile device and the second device is a base station. In stillanother example, both the first device and the second device can bemobile devices.

It is expressly stated that the application of the various steps andfunctions depicted in FIG. 3 are interchangeable between embodiments andthat any order of the steps is possible.

FIG. 6 illustrates a beamforming control system applicable to a massiveMIMO communication system provided by an exemplary embodiment of thepresent disclosure. In the instant embodiment, a first device 60 isconfigured to communicate with a second device 62, which can be a mobilestation, mobile user equipment, or the like. The first device 60 is astationary station, such as a base station or a RRH.

The first device 60 includes an antenna module 601, a radio frequency(RF) module 603, an intermediate frequency (IF) module 605, and abeamforming controller 607. These components are cascaded via mechanicaland/or electrical connections. In the instant embodiment, the antennamodule 601 is coupled to the RF module 603 via cable connection (e.g., Lconnections). The RF module 603 is coupled to the IF module 605 viacable connection. The IF module 605 is coupled to the digitaltransceiver 607.

The antenna module 601 is configured to generate at least onedirectional beam to perform signal transmission and reception operationswith the second device 62. The antenna module 601 comprises an antennaarray, and the antenna array comprises of a plurality of antennaelements. The number of antenna elements in the antenna array dependsupon application, and can range from 2 to 256 antennas. In oneembodiment, the antenna module 601 comprises an antenna array formed by64 antenna elements. The number of cable connections (e.g., Lconnections) deployed between the antenna module 601 and the RF module603, the RF module 603 and the IF module 605, and the IF module 605 andthe digital transceiver 607 depends upon the number of antenna elementsin the antenna module 601. In at least one embodiment, some of the cableconnections are implemented by optical fibers.

The RF module 603, which may include software, hardware, or acombination of both, is configured to up-convert signals sent from theIF module 605 to RF module 603 and transmit RF signals through theantenna module 601, or to receive RF signals from the antenna module601, down-convert the signals and output the signal to the IF module605. The IF module 605, which may include software, hardware, or acombination of both, is configured to sample the IF signals receivedfrom the RF module 603 with a built-in A/D converter and outputs thedigitized data streams to the digital transceiver 607 or to convertdigital streams received from the digital transceiver 607 using a D/Aconverter and outputs converted IF signals to the RF module 603.

The digital transceiver 607, which may include software, hardware, or acombination of both, is configured to determine the optimal beamformingweight associated with the antenna array for a targeted mobile stationand to steer the antenna array of the antenna module 601 to generatebeamforming pattern. The digital transceiver 607 further comprises aphase and amplitude error calibration module 6071, a mask windowgenerator 6073, and a beamforming controller 6075. The phase andamplitude error calibration module 6071 is coupled to the mask windowgenerator 6073. The mask window generator 6073 is coupled to thebeamforming controller 6075.

The phase and amplitude error calibration module 6071 is configured tocompute the covariance matrix based on the signal received at allantenna elements from the second device 62, so as to generate a firstbeamforming weight matrix corresponding to the direction of the seconddevice 62.

In one embodiment, the phase and amplitude error calibration module 6071computes the first beamforming weight matrix based on the covariancematrix using the Singular Value Decomposition (SVD) algorithm.

In one embodiment, the phase and amplitude error calibration module 6071computes the first beamforming weight matrix using the covariance matrixwith noise variance corrected from its first correlating vector.

The mask window generator 6073 is configured to adjust the firstbeamforming weight matrix by applying a mask window to generate a secondbeamforming weight matrix, wherein the mask window generator 6073generates the mask window based on the separation between adjacentsecond devices in the communication system. In the instant embodiment,the mask window generator 6073 is configured to apply an amplitude taperacross the antenna array to reduce sidelobe levels of the second device,thus suppress sidelobe interference to and from other second devices. Inat least one embodiment, the mask window generator 6073 implements themask window by generating a Chebyshev window for minimizing orsuppressing the sidelobe interferences. In one embodiment, mask windowgenerator 6073 implements the mask window by generating a finite impulseresponse (FIR) filter.

The beamforming controller 6075 is configured to steer the antenna arrayand control the beamforming pattern generated to perform transmissionand reception operations with the second device.

The digital transceiver 607 in other embodiments can further includeother modules for performing operations including but not limited tosignal demodulation and decoding operations, and baseband signalprocessing on the received signal after applying beamforming weights(e.g., the second beamforming weight matrix).

It is noteworthy that the system embodiment disclosed herein includesbasic hardware components associated with base stations, RRHs,transmission devices, etc. The basic components can include processors,whether virtual, generic or specialized processors for performingcertain tasks, memory (e.g., cache, RAM, short-term memory, or long-termmemory such as a hard drive or optical disk), input and output devices(e.g., keyboards, touch-sensitive pads, speech sensors, motion sensors,and/or display units), a communication bus for connecting componentstogether and for communication of data. Any known programming languagecan be used to program devices to perform any functionality disclosedherein and different languages will be known to those of skill in theart. In a general system embodiment, a processor and a computer-readablestorage medium or device are included. The medium stores instructions,which when executed by the processor cause the processor to performcertain steps that are disclosed herein. Software modules can alsoinclude code, which when executed by a processor cause the processor toperform certain operations.

FIG. 7 illustrates a massive MIMO communication system architectureprovided in accordance to another exemplary embodiment. A massive MIMOcommunication system 7 includes a first device 70, a plurality of seconddevices 72 a through 72 n. The massive MIMO communication system 7 is aTDD-based data communication system, wherein the uplink and downlinktransmissions are performed in the same frequency band. The first device70 is equipped with an antenna array comprising plurality of antennas701 arranged in an array format (e.g., M by N antenna array). The firstdevice 70 is operable to communicate with the second device 72 a through72 n by performing beamforming operations. The number of second devicesmay range from 2 to 24 units.

In one embodiment, the first device 70 is a base station and the seconddevice is a mobile station. In one embodiment, the first device is a RRHand the second device is a mobile user equipment. In one embodiment, thefirst device is a mobile station and the second device is a basestation. In one embodiment, the first device is a mobile user equipmentand the second device is a RRH. In still another embodiment, the firstdevice I a mobile station and the second device is another mobilestation. The second devices 72 a through 72 n may each be handhelddevices, or a vehicle.

Beams 721 a through 721 n illustrate n beams of electromagnetic energyformed by the antenna module of the first device 70 in a beamformingoperation and are focused in the respective directions of the seconddevices 72 a through 72 n, respectively. Data communication between eachof the second devices 72 a through 72 n and the first device 70 may beinterfered by the neighboring second devices depending upon theseparation between adjacent second devices.

The first device 70 is operable to accurately determine beamformingweights to form beams 721 a through 721 n in respective directions ofthe second device, while able to suppress or mitigate the sidelobeeffect to neighboring second devices. As a result, multiple user devicescan share the same frequency band and the bandwidth efficiency thus canbe maximized using the massive MIMO communication system 7.

Referring to FIG. 8 in conjunction with FIG. 7, FIG. 8 illustrates amethod for beamforming process, which is applicable to a TDD-based MIMOcommunication system such as the massive MIMO communication system 7 ofFIG. 7.

The first device 70 communicates with the second devices 72 a through 72n and performs data communication one second device at a time. At block801, the first device 70 operatively receives an i^(th) signal r_(i)(t)transmitted from one of the second devices 72 a through 72 n, using theantenna array, wherein i is an integer and represents the number of thesecond devices in the massive MIMO communication system. At block 803,the first device 70 determines whether signals from all the seconddevices 72 a through 72 n in the massive MIMO communication system havebeen received. In the instant embodiment, the first device 70 determineswhether the number of signals Ns to be received is zero. When the firstdevice 70 determines that the number of signals to be received is notzero, this indicates that the first device 70 has not yet finishreceiving signals from all the second devices 72 a through 72 n, thefirst device executes block 805. When the first device 70 determinesthat the number of signals to be received is zero, block 813 isexecuted.

At block 805, the first device 70 generates an i^(th) covariance matrixR_(i) based on the i^(th) signal r_(i)(t) received, which corresponds tothe i^(th) second device. At block 807, the first device 70 generatesthe i^(th) first beamforming weight matrix w_(i,1) associated with eachantenna elements of the antenna array based on the i^(th) covariancematrix R_(i). In one embodiment, the first device (e.g., the basestation 40) computes the first beamforming weight matrix w_(i,1) basedon the i^(th) covariance matrix R_(i) using either a singular valuedecomposition (SVD) algorithm or computing from a cross correlationvector in the corresponding covariance matrix R_(i) having noisevariance corrected. At block 809, the first device 70 adjusts the i^(th)first beamforming weight matrix w_(i,1) to generate an i^(th) secondbeamforming weight matrix w_(i,2) corresponding to the targeted seconddevice by applying a mask window. The first device 70 configures themask window based on the channel condition and the separation betweenthe adjacent second devices. In one embodiment, the first device 70implements the mask window with a Chebyshev window. At block 811, thefirst device 70 decreases the number of signals Ns by 1 and returns toblock 803. At block 813, the first device 70 steers the antenna array togenerate the beamforming pattern directed to each of the respectivesecond devices to perform data communication according to the respectivesecond beamforming weight matrix w_(i,2).

For instance, there are two second devices 72 a and 72 b communicatingwith the first device 70, and the number of signals to be received Ns is2. The first device 70 computes the first and the second beamformingweight matrices associated with each of the second devices 72 a and 72 bseparately. In the instant embodiment, the first device 70 receives thefirst signal from the respective second device 72 a, computes the firstand second beamforming weight matrices w_(1,1), w_(1,2) in response tothe first signal received from the second device 72 a. The first device70 decreases the Ns by 1, resulting in Ns=1. Next, the first device 70receives the second signal from the respective second device 72 b,computes the first and second beamforming weight matrices w_(2,1),w_(2,2) in response to the received second signal. After the firstdevice 70 finishes computing and obtaining the first and secondbeamforming weight matrices associated with the antenna array, the firstdevice 70 steers the antenna array to generate beamforming patternsaccordingly.

FIG. 9A illustrates beamforming radiation patterns 901, 903 representingbeams formed by the antenna array of the first device in the directionof the second device (e.g., the mobile stations), wherein the antennaarray is steered using the first beamforming weight matrices w_(1,1),w_(2,1). The first mobile station is located at an azimuth angle of −22degrees with respect to the bore-sight axis of the antenna array. Thesecond mobile station is located at an azimuth angle of 22 degrees withrespect to the bore-sight axis of the antenna array. FIG. 9B illustratesbeamforming radiation patterns 901′ and 903′ represent beams formed bythe antenna array of the first device in the direction of the targetedmobile stations. The antenna array is steered to generate beams withsidelobes being suppressed to a desired level (e.g., −35 dB) using thesecond beamforming weight matrix w_(1,2), w_(2,2).

FIG. 10A illustrates beamforming radiation patterns 1001, 1003, 1005,and 1007 representing beams formed by the antenna array of the firstdevice 70 in the direction of four second devices, wherein the antennaarray is steered using the first beamforming weight matrices w_(1,1),w_(2,1), w_(3,1), w_(4,1) without sidelobe suppression. The first mobilestation is located at an azimuth angle of −35 degrees with respect tothe boresight axis of the antenna array. The second mobile station islocated at an azimuth angle of −15 degrees with respect to the boresightaxis of the antenna array. The third mobile station is located at anazimuth angle of 15 degrees with respect to the boresight axis of theantenna array. The fourth mobile station is located at an azimuth angleof 35 degrees with respect to the boresight axis of the antenna array.FIG. 10B illustrates beamforming radiation patterns 1001′, 1003′, 1005′,1007′ representing beams formed by the antenna array of the first device70 in the direction of the targeted mobile stations. The antenna arrayis steered to generate beams with sidelobes being suppressed to adesired level (e.g., −35 dB) using the second beamforming weightmatrices w_(1,2), w_(2,2), w_(3,2), w_(4,2), respectively.

FIG. 11 illustrates another method of beamforming process provided inaccordance to another exemplary embodiment. The method of beamformingprocess is applicable to a TDD-based data communication system, such asthe massive MIMO system 7 depicted in FIG. 7. FIG. 7 herein merelyserves for illustration purpose, and the scope of the instant embodimentis not limited to the system architecture depicted FIG. 7.

Initially, the first device 70 communicates with the second devices 72 athrough 72 n and performs data communication with one second device(mobile station) at a time to compute the corresponding firstbeamforming matrices for each of the second device (mobile stations 72 athrough 72 n). After all the first beamforming matrices {w_(i,1)} arecomputed, the first device 70 is configured to enhance the performanceof the antenna array by jointly optimizing the second beamformingmatrices {w_(i,2)} for all the mobile stations 72 a through 72 n in themassive MIMO system 7 based on the channel conditions between therespective mobile stations 72 a through 72 n and the first device 70.

At block 1101, the first device 70 with an antenna array receives asignal r_(i)(t) transmitted from one of the second devices (mobilestations 72 a through 72 n). At block 1103, the first device 70generates a covariance matrix corresponding to the respective seconddevice (e.g., one of the mobile stations 72 a through 72 n) based on therespective received signal r_(i)(t). At block 1105, the first device 70generates a first beamforming weight matrix w_(i,1) associated with theantenna array based on the respective covariance matrix generated. Atblock 1107, the first device 70 determines whether all the firstbeamforming weight matrices {w_(i,1)} associated with the second devices(mobile stations 72 a through 72 n) in the massive MIMO system 7 havebeen generated. When the first device 70 determines that not all of thefirst beamforming weight matrices {w_(i,1)} associated with the seconddevices (mobile stations 72 a through 72 n) have been generated, thefirst device 70 returns to block 1101 to determine the first beamformingweight matrix for the next second device; otherwise block 1109 isexecuted. At block 1109, the first device 70 determines that all of thefirst beamforming weight matrices {w_(i,1)} associated with the seconddevices (mobile stations 72 a through 72 n) have been generated, thenthe first device 70 generates a second beamforming weight matrices{w_(i,2)} for all the second devices 72 a through 72 n based on all ofthe first beamforming weight matrices {w_(i,1)} computed earlier, so asto maximize antenna gain toward target second devices (targeted mobilestations) while jointly and effectively cancel the undesired sidelobeinterferences toward other second devices. In one embodiment, the firstdevice 70 may determine the second beamforming weight matrices {w_(i,2)}by applying a zero-forcing (ZF) operation to the first beamformingweight matrices {w_(i,1)}. In another embodiment, the first device 70may determine the second beamforming weight matrix w₂ by applying theMaximum Ratio Combining (MRC) operation to the first beamforming weightmatrices {w_(i,1)}.

At block 1111, the first device 70 steers the antenna array to form thebeamforming patterns in the directions of the second devices (mobilestations 72 a through 72 n) according to the second beamforming weightmatrices {w_(i,2)} to perform the data communication operations with thesecond devices (mobile stations 72 a through 72 n), thereby optimizingthe overall efficiency of the massive MIMO system 7.

FIG. 12A illustrates beamforming radiation patterns 1201 and 1203representing beams formed by the antenna array of the first device 70 inthe direction of the targeted second device (e.g., the mobile stations),wherein the antenna array is steered using the first beamforming weightmatrices w_(1,1), w_(2,1), respectively. The first mobile station islocated at an azimuth angle of −22 degrees with respect to thebore-sight axis of the antenna array. The second mobile station islocated at an azimuth angle of 22 degrees with respect to the bore-sightaxis of the antenna array.

FIG. 12B illustrates beamforming radiation patterns 1201′ and 1203′representing beams formed by the antenna array of the first device inthe direction of the targeted mobile stations. The antenna array of thefirst device is steered to generate beams with a null toward thedirection of the adjacent second device; the null suppressedinterference to a rather deep level (e.g., at least −60 dB) using thesecond beamforming weight matrices w_(1,2), w_(2,2), which are generatedusing the zero-forcing algorithm. The beamforming radiation pattern1201′, generated by the antenna array of the first device, has a peakgain at azimuth angle of 22 degree and a null at the azimuth angle of−22 degrees (depicted by box 1210), while the beamforming radiationpatterns 1203′ generated by the antenna array of the first device has apeak gain at azimuth angle of −22 degree and a null at the azimuth angleof 22 degrees (depicted by box 1220).

FIG. 13A illustrates beamforming radiation patterns 1301, 1303, 1305,and 1307 representing beams formed by the antenna array of the firstdevice 70 in the direction of four second devices, wherein the antennaarray is steered using the first beamforming weight matrices w_(1,1),w_(2,1), w_(3,1), w_(4,1) without sidelobe suppression. The first mobilestation is located at an azimuth angle of −36 degrees with respect tothe boresight axis of the antenna array. The second mobile station islocated at an azimuth angle of −17 degrees with respect to thebore-sight axis of the antenna array. The third mobile station islocated at an azimuth angle of 17 degrees with respect to the bore-sightaxis of the antenna array. The fourth mobile station is located at anazimuth angle of 36 degrees with respect to the boresight axis of theantenna array.

FIG. 13B illustrates beamforming radiation patterns 1301′, 1303′, 1305′and 1307′ representing beams formed by the antenna array of the firstdevice in the direction of the targeted mobile stations. The antennaarray of the first device is steered to generate beams toward targetsecond device while the sidelobes pointing at the positions of theadjacent second devices are suppressed to a very low level (e.g., atleast −60 dB nulls) using the second beamforming weight matricesw_(1,2), w_(2,2), w_(3,2), w_(4,2), which are generated using thezero-forcing algorithm. The beamforming radiation pattern 1301′generated by the antenna array of the first device, has a peak gain atthe azimuth angle of 36 degree and nulls at the azimuth angle of 17,−17, and −36 degrees, respectively. The beamforming radiation patterns1303′ generated by the antenna array of the first device, has a peakgain at azimuth angle of 17 degree and nulls at the azimuth angle of 36,−17, and −36 degrees. The beamforming radiation patterns 1305′,generated by the antenna array of the first device, has a peak gain atthe azimuth angle of −17 degree and nulls at the azimuth angle of 36, 17and −36 degrees. The beamforming radiation patterns 1307′, generated bythe antenna.

An array of the first device, has a peak gain at the azimuth angle of−36 degree and nulls at the azimuth angles of 36, 17, and −17 degrees.

Additionally, the present disclosure also discloses a non-transitorycomputer-readable media for storing the computer executable programcodes of the method for beamforming process depicted in FIGS. 3, 8, and11. When the non-transitory computer readable recording medium is readby a processor, the processor executes the aforementioned method forbeamforming process. The non-transitory computer-readable media may be afloppy disk, a hard disk, a compact disk (CD), a flash drive, a magnetictape, accessible online storage database or any type of storage mediahaving similar functionality known to those skilled in the art.

In summary, the present disclosure provides a method and a system forefficiently and accurately determining beamforming weights for antennaarrays, while the unknown amplitude errors and phase errors across theantenna array elements, are compensated automatically, at the same time.Thereby, enhancing signal transmission and reception accuracy andefficiency.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

What is claimed is:
 1. A method, comprising: receiving, by a firstdevice having an antenna array, a first signal transmitted from a seconddevice; receiving, by the first device, a second signal transmitted froma third device adjacent to the second device; generating, by the firstdevice, a first beamforming weight matrix that corresponds to the seconddevice using the first signal received, and generating another firstbeamforming weight matrix that corresponds to the third device using thesecond signal received; generating, by the first device, a secondbeamforming weight matrix by applying a first window function, andgenerating another second beamforming weight matrix by applying a secondwindow function, wherein the first window function is configured basedon the separation between the second device and the third device, andthe second window function is configured based on the separation betweenthe third device and a fourth device adjacent to the second device andthe separation between the second device and the third device; andsteering, by the first device, the antenna array according to the secondbeamforming weight matrix and the another second beamforming weightmatrix to form a first beam and a second beam toward the second deviceand the third device, respectively.
 2. The method according to claim 1,wherein the step of generating the second beamforming weight matrixcomprises: generating the first window function by generating aChebyshev window, wherein the Chebyshev window is configured based on achannel condition between the first device and the second device; andapplying the first window function to the first beamforming weightmatrix to generate the second beamforming weight matrix.
 3. The methodaccording to claim 1, wherein the step of generating the secondbeamforming weight matrix comprises: generating the first windowfunction by generating a finite impulse response filter, wherein thefinite impulse response filter is configured based on a channelcondition between the first device and the second device; and applyingthe first window function to the first beamforming weight matrix togenerate the second beamforming weight matrix.
 4. The method accordingto claim 1, wherein the step of generating the first beamforming weightmatrix comprises: computing a covariance matrix based on the firstsignal; and generating the first beamforming weight matrix by applyingsub-space decomposition to the covariance matrix.
 5. The methodaccording to claim 1, wherein the step of generating the firstbeamforming weight matrix comprises: computing a covariance matrix basedon the first signal; computing a noise variance of the first signal;correcting the noise variance of a cross correlation vector in thecovariance matrix by subtracting the noise variance from the crosscorrelation vector; and generating the first beamforming weight matrixusing the cross correlation vector.
 6. A beamforming device for a MIMOsystem, comprising: an antenna array configured to receive signals froma mobile device; a processor coupled to the antenna array, wherein theprocessor is configured to: cause the beamforming device having anantenna array, to receive a first signal transmitted from the mobiledevice and receive a second signal transmitted from a second mobiledevice adjacent to the mobile device; generate a first beamformingweight matrix that corresponds to the mobile device using the firstsignal received and generate another first beamforming weight matrixthat corresponds to the second mobile device using the second signalreceived; generate a second beamforming weight matrix by applying afirst window function and generate another second beamforming weightmatrix by applying a second window function, wherein the first windowfunction is configured based on the separation between the mobile deviceand the second mobile device, and the second window function isconfigured based on the separation between the second mobile device anda third mobile device adjacent to the mobile device and the separationbetween the mobile device and the second mobile device; and cause thebeamforming device, to steer the antenna array according to the secondbeamforming weight matrix and the another second beamforming weightmatrix to form a beam and a second beam toward the mobile device and thesecond mobile device, respectively, for performing transmission andreception operation.
 7. The beamforming device for the MIMO systemaccording to claim 6, wherein the processor is configured to generatethe first window function with a Chebyshev window, wherein the Chebyshevwindow is configured based on the channel condition between the firstdevice and the second device.
 8. The beamforming device for the MIMOsystem according to claim 6, wherein the processor computes a covariancematrix based on the first signal, and generates the first beamformingweight matrix by using sub-space decomposition to the covariance matrix.9. The beamforming device for the MIMO system according to claim 6,wherein the processor computes a covariance matrix based on the firstsignal, a noise variance of the first signal, correcting the noisevariance of a cross correlation vector in the covariance matrix bysubtracting the noise variance from the cross correlation vector, andgenerating the first beamforming weight matrix using the crosscorrelation vector.
 10. The beamforming device for the MIMO systemaccording to claim 6, wherein the MIMO system is a time division duplex(TDD) MIMO system.
 11. The beamforming device for the MIMO systemaccording to claim 6 wherein the beamforming device is in a basestation.
 12. The beamforming device according to claim 6, wherein thebeamforming device is in a remote radio head.
 13. A method, the methodcomprising the steps of: receiving, by a first device having an antennaarray, a plurality of receiving signals transmitted from a plurality ofsecond devices; receiving, by the first device, a plurality of secondsignals transmitted from a plurality of third device adjacent to thesecond devices; generating, by the first device, a plurality of firstbeamforming weight matrices and a plurality of another first beamformingweight matrices, wherein each first beamforming weight matrixcorresponding to each respective second device using the respectivereceiving signals, and each another first beamforming weight matrixcorresponding to each respective third device using the respectivesecond signal received; generating, by the first device, a secondbeamforming weight matrix according to the plurality of firstbeamforming weight matrices computed, and generating another secondbeamforming weight matrix according to the plurality of another firstbeamforming weight matrices computed; and steering, by the first device,the antenna array according to the second beamforming weight matrix andthe another second beamforming weight matrix to form a beam and a secondbeam toward the second devices and the third devices, respectively. 14.The method according to claim 13, wherein the step of generating secondbeamforming weight matrix comprises: generating, by the first device,the second beamforming weight matrix by applying a zero-forcingoperation to the plurality of first beamforming weight matrices.
 15. Themethod according to claim 13, wherein the step of generating secondbeamforming weight matrix comprises: generating, by the first device,the second beamforming weight matrix by applying a maximum ratiocombining operation to the plurality of first beamforming weightmatrices.
 16. The method according to claim 13, wherein the step ofreceiving the plurality of receiving signals from the plurality ofsecond devices comprises: receiving, by the first device, the pluralityof receiving signals from the plurality of second devices one at a time.